This invention relates to a sailboat and more particularly to an improved main sail construction for such boats.
As is well known with conventional sailboats, the main sail is supported by a mast and boom assembly. The mast supports the forward vertical edge of the sail while the boom supports the lower horizontal edge of the sail. The boom swings relative to an axis defined by the mast upon sailing and various angles are set by the sailors to obtain the desired motion of the sailboat.
Because of the fact that the force of the sail is transmitted to the hull through the mast, there exists a moment on the hull which can cause the hull to tend to rotate about a vertical axis defined by the mast. This situation may be best understood by reference to FIG. 1 which shows a conventional prior art type of sailboat when in a tacking condition. The sailboat, indicated generally by the reference numeral 11, has a hull 12 on which a mast 13 is supported. The mast 13 is positioned slightly forwardly of the forward edge of a keel 14 which depends from the underside of the hull into the water body. This keel 14 is disposed on a longitudinal center line 15 of the hull 12. To the rear of the hull there is mounted a pivotally supported rudder 16 for steering of the sailboat 11.
A boom 17 is pivotally supported on the mast 13 so that a sail 18 thereon may be disposed at the desired angle to the wind, blowing in the direction shown in the arrow 19 so as to effect movement of the sailboat 11 through the body of water. The sail 18 has a pressure center 21 on which the wind force acts. In the illustrated embodiment, the boom 17 is swung to an angle so as to effect tacking of the sailboat 11. This is movement in a direction generally opposite to or against the wind direction.
The wind across the sail 18 acts through a center of pressure 21 in a direction of force indicated by the arrow A in the vector diagram in this figure. This force resolves into a forward force B and a side thrust force C. Because the center of the mast 13 is offset from the pressure point 21 by a distance L.sub.1, there is generated a turning moment indicated by the arrow M on the watercraft which tends to cause it to rotate and also to side slip. The side slipping action is resisted primarily by the keel 14. As is known the wind force also creates a force about a horizontal axis tending to cause the hull 12 to heal over. The action of the keel 14 also resists this healing action.
Rotation of the hull 12 about the vertical axis defined by the mast 13 is avoided by turning the rudder 16 as shown in this figure so that it generates a force indicated by the force vector E through its action with the water. This force generates a side force D which resists the turning moment M. However, it also provides a drag force F which reduces the forward speed of the hull.
The boom 17 is held against rotation by a force G exerted through a rope on the end of the boom 17 and which acts through a distance L3 from the pivot axis. This distance is greater than the distance L2 from the center of force and hence resists the rotation of the boom 17 and sail 18 so as to permit the force on the sail to achieve the forward motion of the hull 12.
Thus, by mounting the sail so that its forward edge is in line with the mast and with the boom pivoting about this same axis, a considerable drag force is exerted to keep the hull traveling in a forward direction.
It is, therefore, a principal object of this invention to provide an improved mast, sail and boom arrangement for a sailboat. It is a further object of this invention to provide an improved mast, boom and sail arrangement for a watercraft wherein the performance of the watercraft can be substantially improved.
Although it would appear obvious to move the center of the pivot point of the boom 17 to the area in line with the center of pressure, the center of pressure actually shifts as the boom is pivoted. Thus it is not possible to maintain this alignment under all conditions. Furthermore, a situation may arise where the center of pressure can move forwardly of the pivot axis on tacking and this will cause erratic and unsmooth running.
It is, therefore, a still further object of this invention to provide an improved boom, mast and sail arrangement for a watercraft.
One solution to the aforenoted problem is the mounting of the boom for pivotal movement about an axis that is defined apart from the mast. In this way, the pivot axis of the boom need not be coincident with the axis of the mast. However, this gives rise to problems in the design of the hull and also in the design of the pivotal support for the boom.
It is, therefore, a further object of this invention to provide an improved pivotal support for the boom of a sailboat.
It is another object of this invention to provide an improved boom pivotal support which can be well grounded in the hull, but which does not require coincidence with nor utilization of the mast for this pivotal support.
Another problem with sailboats is that the mast is generally mounted in the hull in a relatively permanent fashion. Although it is possible to step the mast, storage then becomes a problem and the actual detachment of the mast from the hull is not a convenient maneuver.
It is, therefore, a still further object of this invention to provide an improved mast and boom arrangement for a sailboat.
It is a yet further object of this invention to provide a mast arrangement for a watercraft wherein the mast is pivotal relative to the boom and can be pivoted into a horizontal position adjacent the boom rather than vice versa.